The acquired immunodeficiency syndrome (AIDS) has become a global pandemic, with cases reported in over 100 countries throughout the world. An intensive research effort has been undertaken in several countries, including the Caribbean, Africa, and India to study the unique epidemiologic, virologic, clinical and immunologic features of AIDS in these areas. In Kinshasa, Zaire, we have identified over 2,000 cases with a male-to-female ratio of 1:1. The disease is predominantly transmitted heterosexually based on a 72% transmission rate among spouses of AIDS patients, high seroprevalence rates among female prostitutes and STD clinic populations. Other epidemiologic studies have demonstrated a 10% infection rate among hospitalized children and an 8% infection rate among blood bank donors in Africa. Case-control studies have confirmed needles, blood transfusions, and vertical transmission from mother to infant. HTLV-III/LAV has been isolated from selected African AIDS patients and genomic studies have demonstrated marked heterogeneity of African isolates compared to North American and European isolates. In clinical studies a diarrheal-wasting syndrome was frequently observed, and 30% of hospitalized acute tuberculosis cases had evidence of infection with HTLV-III/LAV. Immunologic studies have also confirmed a marked elevation of activated CD4 lymphocytes suggesting that exposure to a wide variety of viral and parasitic infection may result in increased susceptibility to HTLV-III/LAV infection. Further studies will examine the natural history of HTLV-III/LAV infection in patients of developing countries with particular emphasis on perinatal transmission, safety and efficacy of immunization programs in HTLV-III/LAV infected children, and genomic changes in viral isolates.